springmvc的DispatcherServlet源码——doDispatch方法解析
DispatcherServlet的doDispatch方法主要用作职责调度工作，本身主要用于控制流程，主要职责如下：
1、文件上传解析，如果请求类型是multipart将通过MultipartResolver进行文件上传解析；
2、通过HandlerMapping，将请求映射到处理器（返回一个HandlerExecutionChain，它包括一个处理器、多个HandlerInterceptor拦截器）；
3、通过HandlerAdapter支持多种类型的处理器(HandlerExecutionChain中的处理器)；
4、调用HandlerExecutionChain的interceptor和handler
5、解析视图、处理异常，渲染具体的视图等；
1. 1：doDispatch方法中：如下：
/** * Process the actual dispatching to the handler. //处理实际调度处理器 * <p>The handler will be obtained by applying the servlet's HandlerMappings in order. //处理程序将通过按顺序的servlet的处理器映射器获得。 * The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters //处理器适配器将通过查询servlet的安装的处理器适配器来获得 * to find the first that supports the handler class. //找到支持处理程序类的第一个。 * <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers //所有HTTP方法都由此方法处理。 这取决于处理器适配器或处理程序 * themselves to decide which methods are acceptable. //自己决定哪些方法是可以接受的。 * @param request current HTTP request //请求当前HTTP请求 * @param response current HTTP response //响应当前的HTTP响应 * @throws Exception in case of any kind of processing failure //任何类型的处理失败的例外 */ protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request; //processedRequest是经过checkMultipart方法处理过的request请求 HandlerExecutionChain mappedHandler = null; boolean multipartRequestParsed = false; WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); try { ModelAndView mv = null; Exception dispatchException = null; try {
//1、文件上传解析，如果请求类型是multipart将通过MultipartResolver进行文件上传解析； processedRequest = checkMultipart(request); multipartRequestParsed = (processedRequest != request);
//2.通过HandlerMapping，将请求映射到处理器（返回一个HandlerExecutionChain，它包括一个处理器、多个HandlerInterceptor拦截器）； // Determine handler for the current request. 确定当前请求的处理程序。 mappedHandler = getHandler(processedRequest); //解析第一个方法 if (mappedHandler == null || mappedHandler.getHandler() == null) { noHandlerFound(processedRequest, response); return; } //3、通过HandlerAdapter支持多种类型的处理器(HandlerExecutionChain中的处理器)； // Determine handler adapter for the current request. 确定当前请求的处理程序适配器。 HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler()); //解析第二个方法 // Process last-modified header, if supported by the handler. 如果处理程序支持，则处理最后修改的头文件。 String method = request.getMethod(); //得到当前的http方法。 boolean isGet = "GET".equals(method); if (isGet || "HEAD".equals(method)) { //处理http的head方法。这种方法应该很少用 long lastModified = ha.getLastModified(request, mappedHandler.getHandler()); if (logger.isDebugEnabled()) { logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified); } if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) { return; } } //4.1调用HandlerExecutionChain的interceptor if (!mappedHandler.applyPreHandle(processedRequest, response)) { return; } //4.2执行解析handler中的args，调用（invoke） controller的方法。得到视图 // Actually invoke the handler. 实际上调用处理程序。 mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); //解析第三个方法 if (asyncManager.isConcurrentHandlingStarted()) { return; } //4.3调用HandlerExecutionChain的interceptor applyDefaultViewName(processedRequest, mv); mappedHandler.applyPostHandle(processedRequest, response, mv); } catch (Exception ex) { dispatchException = ex; }
//5.解析视图、处理异常 processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException); } catch (Exception ex) { triggerAfterCompletion(processedRequest, response, mappedHandler, ex); } catch (Error err) { triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err); } finally { if (asyncManager.isConcurrentHandlingStarted()) { // Instead of postHandle and afterCompletion 而不是后处理和完成后 if (mappedHandler != null) { mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response); } } else { // Clean up any resources used by a multipart request. 清理多部分请求使用的资源。 if (multipartRequestParsed) { cleanupMultipart(processedRequest); } } } }
1.2： DispatcherServlet类中 找到 getHandler
/** * Return the HandlerExecutionChain for this request. //返回该请求的处理程序执行链 * <p>Tries all handler mappings in order. //尝试按顺序处理所有的处理程序映射。 * @param request current HTTP request //请求当前HTTP请求 * @return the HandlerExecutionChain, or {@code null} if no handler could be found //处理程序执行链或代码返回null，如果没有找到处理程序 */ protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception { for (HandlerMapping hm : this.handlerMappings) { if (logger.isTraceEnabled()) { logger.trace( "Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'"); } HandlerExecutionChain handler = hm.getHandler(request); if (handler != null) {
//只会调用一个handler进行处理 return handler; } } return null; }
1.3：我们转而去找HandlerMapping的getHander()发现HandlerMapping是一个接口，找到了实现类
/** * Look up a handler for the given request, falling back to the default //查找给定请求的处理程序，回到默认值 * handler if no specific one is found. //处理程序，如果没有找到特定的。 * @param request current HTTP request //请求当前HTTP请求 * @return the corresponding handler instance, or the default handler //相应的处理程序实例或默认处理程序 * @see #getHandlerInternal //得到内部处理程序 */ @Override public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
//从实现类中获得处理方法 Object handler = getHandlerInternal(request); if (handler == null) { handler = getDefaultHandler(); } if (handler == null) { return null; } // Bean name or resolved handler? //Bean名称或解决的处理程序？ if (handler instanceof String) { String handlerName = (String) handler; handler = getApplicationContext().getBean(handlerName); } //获得处理程序执行链 HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request); if (CorsUtils.isCorsRequest(request)) { CorsConfiguration globalConfig = this.corsConfigSource.getCorsConfiguration(request); CorsConfiguration handlerConfig = getCorsConfiguration(handler, request); CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig); executionChain = getCorsHandlerExecutionChain(request, executionChain, config); } return executionChain; }
1.4:
/** * Build a {@link HandlerExecutionChain} for the given handler, including //为给定的处理程序构建一个链接处理程序执行链，包括 * applicable interceptors. //适用拦截器。 * <p>The default implementation builds a standard {@link HandlerExecutionChain} //默认实现构建一个标准的链接处理程序执行链 * with the given handler, the handler mapping's common interceptors, and any //与给定的处理程序，处理程序映射的常见拦截器和任何 * {@link MappedInterceptor}s matching to the current request URL. Interceptors //映射映射拦截器与当前请求URL匹配。拦截器 * are added in the order they were registered. Subclasses may override this //按照注册顺序添加。 子类可以覆盖此 * in order to extend/rearrange the list of interceptors. //以便扩展/重新排列拦截器列表。 * <p><b>NOTE:</b> The passed-in handler object may be a raw handler or a //注意：传入处理程序对象可能是原始处理程序或 * pre-built {@link HandlerExecutionChain}. This method should handle those //预制链接处理程序执行链。 这种方法应该处理那些 * two cases explicitly, either building a new {@link HandlerExecutionChain} //建立一个新的链接处理程序执行链 * or extending the existing chain. //或扩展现有的链。 * <p>For simply adding an interceptor in a custom subclass, consider calling //为了简单地在自定义子类中添加拦截器，请考虑调用 * {@code super.getHandlerExecutionChain(handler, request)} and invoking //代码:得到父类处理程序执行链（处理器，请求）}并调用 * {@link HandlerExecutionChain#addInterceptor} on the returned chain object. //{@链接处理程序执行链、添加拦截器}在返回的链对象上。 * @param handler the resolved handler instance (never {@code null}) //处理程序解析的处理程序实例（代码从不为空） * @param request current HTTP request //请求当前HTTP请求 * @return the HandlerExecutionChain (never {@code null}) //处理程序执行链（代码从不为空） * @see #getAdaptedInterceptors() //获得适应的拦截器 */ protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) { //如果没有获得则创建一个
HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ? (HandlerExecutionChain) handler : new HandlerExecutionChain(handler)); //获得IP地址及端口后的URL地址 String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
//在HandlerExecutionChain中添加拦截器
// 遍历 SpringMVC 容器的所有拦截器
for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
// 判断拦截器类型，属于 MappedInterceptor，则先匹配路径，否则直接添加 if (interceptor instanceof MappedInterceptor) { MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
//根据lookupPath来获取Interceptor
if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) { chain.addInterceptor(mappedInterceptor.getInterceptor()); } } else { chain.addInterceptor(interceptor); } } return chain; }
结论：处理器执行链=1个hanlder+N个Interceptor
2.1:HandlerAdaptor执行流程（进入方法在1.1）
/** * Return the HandlerAdapter for this handler object. //返回：该处理程序对象的处理程序适配器。 * @param handler the handler object to find an adapter for //传入的参数：处理处理程序对象以找到适配器 * @throws ServletException if no HandlerAdapter can be found for the handler. This is a fatal error. */ //抛出的异常：如果找不到处理程序适配器，则Servlet异常。这是一个致命错误。 protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
//遍历所有的handlerAdapters for (HandlerAdapter ha : this.handlerAdapters) { if (logger.isTraceEnabled()) { logger.trace("Testing handler adapter [" + ha + "]"); }
//调用相应实现的support方法，排在最前面的优先调用 if (ha.supports(handler)) { return ha; } } throw new ServletException("No adapter for handler [" + handler + "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler"); }
3.1:在这里发现了一个接口，找到它 的实现（进入方法在1.1）
/** * Use the given handler to handle this request. //使用给定的处理程序来处理此请求。 * The workflow that is required may vary widely. //所需的工作流程可能会有很大差异。 * @param request current HTTP request //请求当前HTTP请求 * @param response current HTTP response //响应当前的HTTP响应 * @param handler handler to use. This object must have previously been passed //处理程序处理程序使用 此对象必须先前已被传递 * to the {@code supports} method of this interface, which must have //到这个接口的{@code支持}方法，它必须具有 * returned {@code true}. //已返回{@code true}。 * @throws Exception in case of errors //异常情况下出错 * @return ModelAndView object with the name of the view and the required //ModelAndView对象具有视图的名称和必需 * model data, or {@code null} if the request has been handled directly //模型数据，或{@code null}，如果请求已被直接处理 */ ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;
3.2接口的各个实现
3.3这里我们用的是SimpleControllerHandlerAdapter
public class SimpleControllerHandlerAdapter implements HandlerAdapter { @Override public boolean supports(Object handler) {
//判断是否是Controller类 return (handler instanceof Controller); } //执行Controller的handleRequest方法 @Override public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { //本质是执行Controller的handleRequest方法 return ((Controller) handler).handleRequest(request, response); } @Override public long getLastModified(HttpServletRequest request, Object handler) { if (handler instanceof LastModified) { return ((LastModified) handler).getLastModified(request); } return -1L; } }
